The background of the invention is discussed briefly in the following.
3GPP specifies a new architecture for IP Multimedia (3GPP, Third Generation Partnership Project; IP, Internet Protocol). IP Multimedia will offer subscribers new services like video-calls and conferences, but also traditional services like speech calls will be an important feature. The technology is based on SIP (SIP, Session Initiation Protocol).
A prerequisite for IP Multimedia services to become popular among end users and profitable to the operators is to find a fair and efficient way of charging for the offered services. This is however not easy, due to the new technology and architecture, which is fundamentally different compared to traditional telecom networks.
In traditional telecom networks, the distance between the involved parties, and the used access types e.g. mobile access or fixed access, has a significant influence on the tariff of a service. It is also customary that the calling party pays for a call, at least to the point in the network, which can be identified by the called party's number e.g. E.164 number.
In some countries, like the US, mobile subscribers have to pay for the access part i.e. airtime of a call, also when receiving a call. However, this charging model has proved to be less efficient than a model where the calling party pays for the whole call, since called subscribers often refuse to accept incoming calls if they have to pay for them.
When allowing charging models like the calling party A pays for the call some communication between the networks (e.g. originating, terminating and in some cases transit networks) is needed. In mobile communication networks one can see on the number where one is calling and in some cases one can see if the called party is a mobile or a fix user. Rating/charging for the calling party is done in his/her home network and the charging/billing system can see the destination of the call on the called party number and can rate the call accordingly. The terminating network will then charge the originating network for terminating the call. This charging process is done from the terminating network to the originating network via the transit networks.
In an IP-based multimedia system (IMS) there is no possibility to see on the called party what access type, for example fixed/mobile, the called party is using and thus the call/session can not be rated without knowing the cost for the terminating network to terminate the call. In this case home network of the called party has to check with home network of the calling party if it would like to take the charge for termination the call/session and the tariff/cost for it.
For free phone numbers or premium rate numbers the same problem applies. In these cases the called party is charged for the whole call or parts of the calls. In this case must the home network of the called party contact the home network of the calling party and indicate that the called party is willing to take the charges or a part of the charges.
The communication between the home networks need to be done on a new interface or on an existing interface dedicated for charging.
Future operators of IP Multimedia networks have indicated that they want to follow the same charging principles as in traditional telecom networks, e.g. calling party pays for the whole call and the charging is dependent on access type. According to legislation in most countries, it's not possible to charge for a service, if it's not possible for a subscriber to know the tariff of the service prior to usage.
It will be especially challenging to charge for IP Multi-media sessions, since it will be impossible for a calling party to determine based on the called party address, i.e. a SIP URL (e.g. Johan.Lundstrom@company.com), the distance and the access type currently used by the called party. Even though operators may in the future not charge based on the distance anymore, the access type will certainly have an impact on the charging, since some access types, for example mobile, will always be more costly for the operators to provide than others.